Coots fly across the water of the flooded Yolo Bypass - part of the Pacific Flyway - on Tuesday, February 2, 2010.
The Yolo Bypass is flooded for the first time since 2006 due to high water in the Sacramento River following recent storms. As a result, it's become a vast wetland filled with new-hatched insect blooms feedings schools of native salmon and splittail fish -- and even more waterfowl. The transformation highlights an ongoing debate over a possible broader role for the bypass in restoring the Delta.

Photo: Randy Pench, Sacbee.com

Coots fly across the water of the flooded Yolo Bypass - part of the...

The amount of water pumped out of the Sacramento-San Joaquin River Delta would have to be cut in half if vulnerable fish populations are going to be preserved for future generations, a state report declared Tuesday.

The 190-page study by the State Water Resources Control Board is nonbinding, but it could shape how communities from the Bay Area to San Diego divvy up California's most precious resource.

The document, issued by the five-member board after nine months of scientific study, determined that 75 percent of runoff from snowpack and rainfall would need to funnel through the delta to San Francisco Bay and the ocean in order to sustain the estuary's most important wildlife and habitats, known in legal parlance as "public trust" resources.

Right now, about 50 percent of the state's runoff flows through the delta all the way to the ocean. The other 50 percent goes to cities and farms. Raising the flow into the ocean from 50 percent to 75 percent would require taking away roughly half of what cities and farms now get, according to the report.

"The board has finally put to rest the argument about whether the delta needs more water," said Cynthia Koehler, water legislative director with the Environmental Defense Fund. "You can't divert 50 percent of the flows and think the fish and ecosystem are going to be just fine."

The other view

Many of the largest water districts in California lambasted the report as one-sided and contended that higher delta flows and less pumping would devastate the economy and hurt farmers grappling with water cutbacks first stipulated by a federal judge in 2007 and fought over ever since.

"The information certainly is interesting and informative ... but it's immaterial," said Tom Birmingham, general manager of Westlands Water District, a sprawling agricultural zone in the Fresno area. "Protecting the public trust resources are not the only goals of the planning processes."

The delta, at the confluence of the state's two largest rivers - the Sacramento and San Joaquin - is the hub of California's vast water system. As such, it has been the source of increasing tension between fishermen, farmers, city leaders and federal and state politicians trying to protect their water rights.

The state study, mandated last year by the Legislature as part of a sweeping water reform package, does not carry any regulatory weight, but it offers a basis for changing how much water is delivered to 23 million Californians downstream of the delta, not to mention users who remove water from the system before it reaches the estuary.

Along with pollution, climate change, aging infrastructure and invasive species, excessive water exports over the past several decades have pushed the delta and certain fish species into a death spiral.

More studies to come

The research purposely weighed only the needs of a healthy habitat for crashing species like the longfin smelt and not the interests of cities and farms. Later studies, part of a broad-based effort to craft a management plan for the delta, will seek to balance a stable water supply with rehabilitation of the ecosystem.

Environmentalists, fishing groups and delta residents firmly support allowing more water to flush through the delta, arguing that higher flows mean cooler, deeper, less salty and less polluted water for fish spawning and migration. It would also help steer fish away from the giant pumps that entrap and kill vulnerable juveniles.

Koehler's group and others say conservation, desalination and water recycling could drastically reduce dependence on the delta.

Officials at Zone 7 Water Agency, which serves nearly 200,000 residents in eastern Alameda County, say they are willing to do their part in reducing dependence on the delta and are exploring a regional desalination project. But with 80 percent of its supply from the delta, the district is in a difficult position.

"We'll always have to rely on the delta for the majority of our water," said spokeswoman Boni Brewer.

Less clear is how delta flow criteria could also affect so-called upstream users, such as the San Francisco Public Utilities Commission or East Bay Municipal Utility District, which tap into rivers before they pour into the delta.